<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        .con{
            /* width: 1000px; */
            display: flex; 
            border: 1px solid red;
        }
        .item1{
            width: 200px;
            height: 200px;
            border: 1px solid rebeccapurple;
        }
        .item2{
            flex: 1;
            /* width: calc(1000px - 200px); */
            border: 1px solid rebeccapurple;
            background-color: red;
        }
    </style>
</head>
<body>
    <div class="con">
        <div class="item1">1</div>
        <div class="item1">1</div>
        <div class="item2">2</div>
    </div>
</body>
</html>